The present invention relates to a seat-load measuring device for measuring a weight of a passenger and an object sitting on a car seat.
In a passenger car, control operations of winding a seatbelt and inflating an airbag are performed based on whether or not a car is occupied, whether an adult or a child is sitting on the seat, whether or not a child-seat is mounted, and the like. To achieve this purpose, a seat-load measuring device has been increasingly used for measuring the weight of the passenger and the object sitting on the car seat.
Such a seat-load measuring device has a configuration such that a load measuring section provided under the seat measures the overall weight of the seat, the passenger, and the object on the seat, and then a true load on the seat is obtained by subtracting the weight of the seat from the above overall weight. A strain gauge is typically used as a sensor of the load measuring section.
A measured value varies with noise caused by a motion of the passenger on board or acceleration of the car. Thus, the seat-load measuring device is required to remove such noise so as to maintain measurement accuracy within a predetermined range. In addition, a large load change takes place in a short period of time when the passenger is in a half-sitting posture on the seat upon opening and closing a door, or trying to pick something up. Even when such a large load change takes place, the seat-load measuring device is required to maintain the measurement variance within an acceptable range.
To achieve this, merely providing the measuring device with a low-pass filter is sufficient to remove small load changes. However, the low-pass filter with a large time constant, which can ignore a large temporary load change, has a risk of failing to detect a true load change during moving.
Also, it is necessary to measure the load as quick and accurate as possible to start the seatbelt control when the passenger sits on the seat. However, the above slow response load measuring device does not meet this requirement.
In view of these problems, the object of the present invention is to provide the seat-load measuring device that can perform a quick load measurement when the passenger sits on the seat, and become relatively insensitive to a load change after the passenger sits on the seat.
Further objects and advantages of the invention will be apparent form the following description of the invention.
The first aspect of the invention for solving the above problems provides a seat-load measuring device for measuring a weight of a passenger and an object sitting on a car seat. The measuring device has a function in which, when a load exerted on the seat exceeds a predetermined value, for example, when the passenger gets in or out of a car, an output from the load sensor through a slow response system is taken first as a measured load, and then the load sensor output through a fast response system is taken as the measured load.
According to the first aspect, the measuring device first determines whether or not a change in the load exerted on the seat goes beyond a predetermined value. When the seat is unoccupied or the passenger remains sitting on the seat in a normal manner, the load change is small even if the load varies. A large load change takes place when the passenger gets in or out of the car, or leaves the seat, for example, when trying to pick something up, or pushes the seat to get in the car. The first aspect is provided for determining if the latter case occurs.
In the latter case, the measuring device determines if the load change is temporary, and keeps the measured load unchanged if it is the case. At a point when the measuring device confirms that the load change is not temporary, the measuring device quickly starts to take an output from the load sensor through the fast response system.
To achieve this, even when the change in the load exerted on the seat exceeds the predetermined value, the measured load does not immediately reflect the change in the load, but takes an output from the load sensor through the slow response system as the measured value for the time being. Here, the slow response system means a filter with a slow response time or a system that holds a measured load, and also has a function of a low-pass filter.
Accordingly, for a certain period of time (which can be fixed or variable), the output from the load sensor is not taken as the measured load, or the output through the slow response is used as the measured load. Thus, if the passenger gets out of the seat when trying to pick something up or pushes the seat with a hand, for example, when getting in the car, the load associated with these instances is not used as the measured seat load.
If the measured value still continues to exceed the predetermined value after the above certain period of time, the output from the load sensor is taken through the fast response system and is set as an updated measured load, assuming that the passenger actually gets in or out of the car. Here, the fast response system means a filter with a fast response time, and also has a function of a low-pass filter.
According to this aspect, the output from the load sensor is processed through the slow response system when the load change is temporary, and through the fast response system after the load change continues for a fixed or variable predetermined time. Therefore, the measured load quickly comes close to the output from the load sensor when the passenger gets in or out of the car, while avoiding a situation in which the load change unrelated to getting in or out of the car is taken as the measured load.
The second aspect of the invention for solving the above problems provides a device in the first aspect further having a plurality of filters with different time constants. The device is capable of switching a state in which the output from the load sensor through the slow response system is taken as the measured load to another state in which the output from the load sensor through the fast response system is taken as the measured load. The switching timing is determined on the basis of a difference between outputs through at least two filters, one with a small time constant and the other with a large time constant.
The filter with the small time constant as mentioned above includes the one with a zero time constant, that is, the one that does not function as a filter. The difference between two outputs of the load sensor, one processed through the filter with the small time constant and the other processed through the filter with the large time constant, changes from xe2x80x9csmallxe2x80x9d to xe2x80x9clargexe2x80x9d to xe2x80x9csmallxe2x80x9d when the passenger gets in or out of the car. That is, a state of the large difference continues for a certain period of time. On the other hand, the state of the large difference continues only for a short period of time when the passenger is in a half-sitting posture to try to pick something up, or pushes the seat with a hand upon getting in the car.
By utilizing this feature, the measuring device determines whether the difference is caused by the passenger getting in or out of the car, or by a temporary load change. Only when the former is the case, the measuring device switches the state in which the output from the load sensor through the slow response system is taken as the measured load to the other state in which the output from the load sensor through the fast response system is taken as the measured load. Thus, the measuring device allows the measured load to quickly come close to the output from the load sensor when the passenger gets in or out of the car, while avoiding a situation in which the load change unrelated to getting in or out of the car is taken as the measured load.
In this means, two outputs of the load sensor, one through the filter with the small time constant and the other through the fast response system, may be the same, but are not necessarily the same. Likewise, two outputs of the load sensor, one through the filter with the large time constant and the other through the slow response system, may be the same, but are not necessarily the same. That is to say, xe2x80x9cat least two filters, one with the small time constant and the other with the large time constantxe2x80x9d in this aspect are used for determining the timing based on the difference, and the outputs through these filters are not necessarily used as the measured load. An output from the load sensor through the slow response filter or the fast response filter, which are different from these filters, may be used as the measured load.
Furthermore, the fast response system and the slow response system may be configured with different filters so as to be used by switching them, or may be configured with a single filter by switching circuit constants of the single filter (or coefficients in the case of a digital filter) so as to create the fast response system and the slow response system, and be used by switching them.
The third aspect of the invention for solving the above problems provides a device in the second aspect further comprising the slow response system that has a digital filter for delaying a response. The device has a function that, when a state in which the output from the load sensor through the slow response system is taken as the measured load is switched to another state in which the output through the fast response system is taken as the measured load, a value of the digital filter is changed so that the output through the slow response system comes close to that through the fast response system.
In the second aspect, there is a case in which the output from the load sensor through the slow response system is taken as the updated measured load to avoid the disturbance caused by noise and the like after the measurement is switched to a stable state from a state in which the output from the load sensor through the fast response system is taken as the measured load. At this moment, however, as the filter with the large time constant, which is used as the slow response system, does not respond quickly, the output through the filter is sometimes deviated from that of the load sensor.
In the third aspect, therefore, the value of the filter in the slow response system is changed so that the output load of the slow response system comes close to that of the fast response system when the state in which the output from the load sensor through the slow response system is taken as the measured load is switched to the other state in which the output from the load sensor through the fast response system is taken as the measured load. Since this filter is the digital filter, the above two output loads may be forced to agree with each other by replacing all load values stored in the filter (i.e., values stored in the corresponding shift registers) in the slow response system with those stored in the filter in the fast response system. Alternately, the output load of the slow response system may be changed closer to that of the fast response system by changing response coefficients of the filter in the slow response system so as to make the response time faster. Thus, even if the output of the filter with the large time constant is used as the measured load hereinafter, the output is not significantly deviated from the actual value.
The phrase xe2x80x9cwhen the state in which the output from the load sensor through the slow response system is taken as the measured load is switched to the other state in which the output from the load sensor through the fast response system is taken as the measured loadxe2x80x9d means a switching instance, and more particularly, means an instance of the exchange, and the instance can be when at least the measured load is switched to the output from the load sensor through the fast response system or when the predetermined time period elapses after the switch occurs.
The fourth aspect of the invention for solving the above problems provides a seat-load measuring device for measuring the weight of the passenger and the object sitting on the car seat. In the measuring device, when the measured load exceeds a predetermined value, the output from the load sensor through the system, which has the slower response than the system for the case in which the measured load is smaller than the predetermined value, is taken as the measured load.
In the fourth aspect, if the measured load exceeds the predetermined value, that is, the passenger is assumed to be on board, the load change associated with the moving car or changes in the passenger""s motion is likely to become a noise. To remove such a noise, the output from the load sensor through the slow response system is used as the measured load.
On the other hand, if the measured load is equal to or smaller than the predetermined value, that is, the passenger is assumed not to be on board, the load change is small and the noise is also insignificant. Thus, the output from the load sensor through the fast response system is used as the measured load, thus allowing the passenger to be detected quickly upon getting in the car.
An operation of xe2x80x9cthe output of the load sensor through the slower response system is used as the measured loadxe2x80x9d can be done by switching response systems with different response times to each other, or by changing the response time in the single response system. This aspect can be used in combination of the foregoing first to third aspects, or the fifth to seventh aspects described later.
The fifth aspect of the invention for solving the above problems provides a seat-load measuring device for measuring the weight of the passenger and the object sitting on the car seat. In the measuring device, when the load exerted on the seat exceeds a predetermined value, for example, when the passenger gets in or out of the car, a previously measured value obtained before the load change is taken and held as the measured load for a predetermined period of time, then after that, the measured value is updated by a freshly measured value. The predetermined period of time is adjusted according to the change in the load exerted on the seat.
In the fifth aspect, which is a modification of the first aspect, the previously measured value obtained before the load change is held as the measured load for the predetermined period of time, and the value measured after the period of time is used as the updated measured load. The term xe2x80x9cthe measured valuexe2x80x9d means either of the output from the load sensor or the output from the load sensor through the filter.
xe2x80x9cThe predetermined time periodxe2x80x9d can be adjusted in accordance with the change in the load exerted on the seat. That is, a previously measured value obtained before the load change is held as the measured load while the load change is unstable, and the newly measured value is used as the updated measured load when the load change is stabilized, or when the predetermined time period elapses after the load change is stabilized.
According to the fifth aspect, when the passenger gets out of the seat when trying to pick something up, or pushes the seat with a hand, for example, when getting in the car, the previously measured value is held as the measured load since the load change is unstable, and the newly measured value (which is substantially the same as the previously measured value) is used as the measured load when the unstable load change does not exist any more. On the other hand, since the load change is stable when the passenger gets in or out of the car, the newly measured value is used as the updated measured load after the predetermined time period.
The sixth aspect of the invention for solving the above problems provides a measuring device in accordance with the fifth aspect, further comprising a plurality of filters with different time constants. The predetermined period of time is determined on the basis of a difference between outputs of at least two filters, one with the small time constant and the other with the large time constant.
The difference between two outputs of the load sensors, one through the filter with the small time constant and the other through the filter with the large time constant, changes from xe2x80x9csmallxe2x80x9d to xe2x80x9clargexe2x80x9d to xe2x80x9csmallxe2x80x9d when the passenger gets in or out of the car. That is, a state of the large difference continues for a certain period of time. On the other hand, the state of the large difference continues only for a short period of time when the passenger is in a half-sitting posture to try to pick something up, or pushes the seat with a hand upon getting in the car. By utilizing this feature, the measuring device determines whether the difference is caused by the passenger getting in or out of the car, or by the temporary load change, which adjusting the predetermined period of time is based on.
The seventh aspect of the invention for solving the above problems provides a measuring device in accordance with the sixth means, further including digital filters as the above filters. The device has a function in that the output through the filter with the large time constant is used as the measured load after the predetermined period of time.
The seventh aspect has the same effects as does the third aspect.